1. Field
The present disclosure generally relates to the field of liquid crystals. More specifically, the present disclosure relates to a liquid crystal device comprising at least one confining substrate, a liquid crystal bulk layer presenting a surface-director at a bulk surface thereof, wherein an orthogonal projection of said surface-director on said substrate, termed projected surface-director, presents a preferred orientation in a geometrical plane parallel to said substrate, termed preferred in-plane orientation, and a surface-director alignment layer comprising a chiral smectic liquid crystalline material arranged to interact with the bulk layer at said bulk surface, said surface-director alignment layer being a dynamic alignment layer directly controllable by an applied electric field to perform an in-plane switching in the surface-director alignment layer for accomplishing, as a direct consequence of this in-plane switching and the interaction at the bulk surface, an in-plane switching of said preferred in-plane orientation of the projected surface-director.
The disclosure also relates to a method for manufacturing said liquid crystal device.
2. Description of Related Art
The published international patent application No. WO 00/03288 describes the so-called ECS (Electrically Commanded Surfaces) principle.
According to the ECS principle, a separate thin liquid crystalline polymer layer, such as a chiral smectic liquid crystalline polymer layer, preferably a ferroelectric (chiral smectic C phase, SmC*) liquid crystalline polymer layer, is deposited on the inner surface(s) of one or both of the substrates confining a liquid crystal bulk material in a conventional sandwich cell.
The chiral smectic liquid crystalline polymer layer acts as a surface-director alignment layer imposing a planar or substantially planar alignment on the adjacent liquid crystal bulk material. More specifically, when applying an external electric field across the cell—and thereby across the surface-director alignment layer—the molecules in the separate chiral smectic liquid crystalline polymer layer will switch. The change of the dynamic surface-director alignment layer in response to the electric field is referred to as the “primary surface switching”. This primary surface switching results in its turn, via elastic forces (steric coupling), in a switching of the preferred molecular orientation within the bulk volume of the liquid crystal bulk material confined between the substrates. This secondary switching is referred to as the “induced bulk switching”. This induced bulk switching is an in-plane switching. Thus, the molecular switching in the dynamic surface-director alignment layer will be transmitted into the bulk volume via elastic forces at the boundary between the separate surface-director alignment layer and the bulk layer, thus resulting in a relatively fast in-plane switching of the bulk volume molecules mediated by the dynamic surface-director alignment layer.
Normally, the electric field would be applied across the entire cell, including the liquid crystal bulk layer, but as far as the basic principle of the ECS principle is concerned, any presence of the electric field over the liquid crystal bulk layer is not of primary importance, although in certain applications such presence may be useful.
The chiral smectic liquid crystalline polymer layer, i.e. the dynamic surface-director alignment layer, may be a chiral smectic C (SmC* or SmCA*) material or a chiral smectic A (SmA*) material. Thus, the response of the dynamic surface-director alignment layer to an applied electric field may be ferroelectric, antiferroelectric or paraelectric, respectively.
The ECS layer should preferably be very thin (100-200 nm). Furthermore, in order to keep the ECS layer and its operation intact, the material of ECS layer should be insoluble in the liquid crystal bulk material.
The use of an ECS layer in a liquid crystal device provides a fast in-plane switching and a comparatively high image contrast. However, it would be desirable to improve the contrast even further.